• Style & appearance
• Product data
• Design considerations
• Installation & Maintenance

Style & appearance

Photographs

Product photograph

Dimensions (mm)
Sump Unit	Silt Box
One Piece Unit	Two Piece Unit
Access Top

Product data

Trafficking

• City roads
• Town centres
• Urban areas

Features and benefits

• One or two piece system available
• 2 depths dependant on drainage requirements
• Resistant to frost, ageing and road salts
• Minimal disruption during installation compared to other systems
• Supplied in pallet packs for easy manoeuvrability on site
• Large inlet openings for fast efficient drain off

Product range dimensions

Flow capacities

Accessory units – dimensions

Design considerations

General principles

The aim is to ensure prompt and cost-effective removal of surface water during and immediately after rainfall.
Optimum balance of cost efficiency and performance is achieved by parallel drainage runs at 30-35 m intervals across drainage area.
Wider spacing between runs is possible, but (dependent in rainfall intensity) may result in slower removal of surface water and increased costs – for extra outlets and additional underground pipework.

Maximum recommended width of the drained area to any one run is 35 metres. Choose slot or grid unit options according to type and frequency of anticipated trafficking. While these options do not affect the design of drainage performance, the choice of nominal bore (Safeticurb 125 mm or 150 mm; Clearway 150 mm only) does affect capacity and self-cleansing capability.

Self-cleansing velocity A flow rate of 0.76 metres per second is normally sufficient to avoid silt settlement in the channel inverts. Longitudinal gradients required to achieve this velocity are: for 125 mm bore (Safeticurb only): 0.75% (1:133) for 150 mm bore (Clearway or Safeticurb) 0.6% (1:167). Both systems will operate successfully at slacker gradients, though occasional flushing out may be needed.

System drainage areas:
Gradient against rainfall intensity by nominal bore

Installation design – units

General principles

All units are unreinforced: protect from stresses caused by thermal expansion of cementitious paving materials. Leave 1mm gap between each unit to prevent damage from thermal expansion of the units themselves.

Expansion joints MUST be installed on each side of drainage runs in concrete pavements or those incorporating a cement bound/lean mix concrete roadbase.

DO NOT place these joints directly adjacent to any trafficked unit as this would allow units to rock under trafficking and may allow water ingress into the base or sub-grade.

• Recommended position of joints (minimum distances):
• 600 mm from Clearway/Safeticurb units (see Figs 12-14).
• 125 mm from Highway units (see Figs 5-6).

Note:
As Highway units are not regularly trafficked, expansion joints could be placed directly against them. However, 125 mm distance is recommended to avoid ingress of water between the unit and carriageway construction.

Base foundations

Recommended typical foundations are:

• for Clearway/Safeticurb: minimum 150 mm depth of ST4 concrete with a 25 mm bed of Class 1 mortar (1:3 cement: sand) to allow easy adjustment of units to line and level.
• for Highway: minimum 75 mm of concrete.

Note:
Strength, overall depth and width of the base may need to be increased when laid on low - strength sub-grades.

Haunching

Recommended typical haunches (to within 100 mm of top unit) are:

• For Clearway/Safeticurb: ST4 concrete.
• For Highway: ST1 concrete minimum 125 mm width.

General principles

Details of outlet units an inspection access differ according to which linear drainage system is used.
In any system, silt or detritus should normally be prevented from entering the main drainage sewer. An outfall chamber is required to enable silt collection before onward connection to a sewer.

Types of outfall chamber

• trapped precast concrete, clay or plastic gully pots. Gully pot capacity may be insufficient for some largerlinear drainage installations.
• Purpose-built brick or concrete inspection chamber.
• Precast concrete manhole rings.
• Dedicated sump unit.

Select outfall pipe diameter/gradient

Care should be taken to ensure sufficient capacity.

Highway

Standard outlet formed using two base outlet units (in place of standard base units) to give full width rectangular outlet 400x275 mm. (shallow and deep base outlet units available). Positioning is not critical, but should allow access for suction pipe from gully emptier.

Discharge capacity may be increased by installing more than one pair of Base Outlet units discharging into the same outfall chamber.
For larger schemes, chambers to be detailed in accordance with The Specification for Highway works, clauses 507 and 508. For larger outfall pipes it may be necessary to incorporate a manhole access at rear of run.

Clearway/Safeticurb

Select outfall chamber, pipe dimension and pipe gradient to suit system capacity. Position a silt box top on two courses of engineering brickwork over the selected outfall chamber/silt trap to give access (via the silt box lid) for silt removal.

HydroKerb sump unit

With hinged, removable lid for inspection access, is placed over sump unit in place of standard top units. (See page 143 for alternative option).

Mini Highway sump unit

With hinged, removable lid for inspection access, is placed over inflow unit in place of standard top units.

Radii

Highway/Mini Highway:

• To form external radii of 25 metres or less (minimum 6 m), special radius units should be used (see table below). As these do not cover all individual radius dimensions, some slight gaps are required between units as indicated in Highway radii gap widths table, below.
• For external radii greater than 25 metres, lay straight units with open joints.
• To form internal radii (minimum 6 metres), use 7/6 internal radius units.

Clearway/Safeticurb:

• Where necessary, standard (straight) units may be laid to form radii or bends.
• Safeticurb units: alignment ring within bore acts as a former for infill mortars to seal joint.

Crossings

Highway/Mini Highway:

• Use crossing base units to carry drainage runs under side roads/vehicular crossing points. Grid units available.

Safeticurb (DBK unit only):

• To continue linear drainage at road junctions, kerb crossing points (pedestrian/vehicular), use transition units to reduce kerb height to road level. These connect with standard grid or slot units as necessary.

Junctions/sharp bends

Clearway/Safeticurb:

• Use silt box top at outlets or with suitable uPVC pipe fittings (cut to fit) to form junctions or sharp bends.

Highway radii gaps widths